And everyone would get called on. Elizabeth Warren made sure, leaving nothing to chance in her contracts class. While Warren, always in motion, zipped questions at the 80 first-year students, teaching assistants tracked her using notecards. At the break, they slipped her cards with the names of any students she had missed.

For incoming Harvard Law students accustomed to the comfort of an undergraduate liberal arts seminar, it was a shock to the system. “A cold intellectual shower first thing in the morning,” is how Angela Littwin, a 1L in the fall of 1999, still remembers it.

Warren’s classes required more preparation than most. Students could not defer when she called on them with a question, even if they had not done the reading. The entire hall listening, Warren would stay with them, feeding crumbs of information while continuing to press, habitually pulling her rimless glasses off and on.

“There are lots of people who are that demanding and just kind of mean about it,” said Littwin, now an assistant law professor at the University of Texas. “The trick is to be that demanding and still have your students love you.”

Not that any of this emerges on the trail as Warren campaigns to unseat Senator Scott Brown. She has aired more than a dozen TV and radio ads without mentioning Harvard even once, and she tiptoes around it on the stump.

‘I’m teaching a really hard point and you can see students’ faces are like — they look grim. Struggling. And, then, it clicks.’

That is partly because Warren’s nearly two decades as a Harvard Law professor fit less neatly into a tight campaign narrative than her humble origins or her advocacy for the middle class, although that advocacy grew out of her research on bankruptcy.

But it is mostly because of the effectiveness with which Warren’s opponent has wielded it as a cudgel against her. In debates, Brown has mentioned Warren’s Harvard salary — tax returns show it was close to $350,000 her last full year — and criticized her teaching workload. Harvard Law professors spend, on average, five hours a week in the classroom, with the bulk of their time reserved for research, writing, student advising, and administrative tasks.

“Professor,” as Brown uses it, has become a fraught title, something less than an honorific — an image conjured of Warren as Harvard elitist, liberal ideologue, scolding schoolmarm.

At Harvard, she is known as none of those. Widely admired by students and faculty, she is considered tough but fair, whip smart but warm, inspiring, and accessible. Warren, who is on leave, has won student-nominated teaching awards at four of the five universities where she has taught, including Harvard’s Sacks-Freund Award — twice — as voted by the graduating class.

Top law schools hire for scholarship, not teaching prowess, and some of Harvard’s more than 80 tenured law professors scoff at classroom awards, considering them popularity contests favoring charisma over rigor. But Warren is both charismatic and rigorous, making her “hugely admired as a teacher by students and faculty alike,” said Richard Fallon, also a two-time teaching prize winner. She teaches through constant questioning — known as the Socratic method — without lecturing or telegraphing the answers she seeks. “It’s a gift,” he said. “I don’t have it.”

Warren’s studies of consumer bankruptcy — exposing it not as the domain of the poor and rash but as a middle-class phenomenon triggered by job loss, illness, or divorce and exacerbated by financial laws — earned her notice among Ivy League deans and Washington policymakers. But teaching came first, long before Warren considered the law or the plight of the middle class.

“I always knew that I wanted to teach. I knew that when I was 6 years old,” said Warren, who was a school speech pathologist before going to law school.

In a rare interview about Harvard, Warren sprang to life describing the moment when students make an intellectual discovery.

“I get to watch light bulbs go off,” she said, whispering “light bulbs” like a cherished secret. “I can look out in a room and I’m teaching a really hard point and you can see students’ faces are like — they look grim. Struggling. And, then, it clicks.”

One, then another. “Ping! Ping-ping! Ping-ping-ping!”

Warren popped up in her chair, pinching at the air with each “ping” as if catching flies with chopsticks. “It’s exhilarating,” she said.

Warren’s laptop ban, a rarity at Harvard Law, is not about preventing students from scrolling Facebook or shopping online but from taking dictation. She wants to make sure they are engaged in a rapid-fire, roomwide conversation — and not too busy taking notes for those light bulbs to go off.

“Even though I wasn’t completely aware of it at the time, in taking the exam I knew the bankruptcy code like the back of my hand,” said Patrick Tierney, who took a bankruptcy class with Warren as a 2L in fall 2008. Normally a dry class, Warren’s section had a waiting list.

That semester, the US economy imploded, and Senate majority leader Harry Reid phoned Warren to ask her to lead congressional oversight of the emerging bank bailout, known as the Troubled Asset Relief Program. Warren struggled to make out his famously mild voice while trying to welcome students to her Linnaean Street home for a discussion of public interest careers, write a check to the delivery guy from Redbones (“they have good ’cue, mm-hm,” she sighed), and keep her barking golden retriever from devouring the barbecue.

At the end of the semester, Tierney was among the students who helped research the history of financial reform for the first of 24 papers that Warren’s relief program oversight committee produced. After graduation, he followed her to the nascent Consumer Financial Protection Bureau, which Warren helped Congress write into existence and spent a year assembling.

Warren conducted weekly staff meetings even as the bureau grew from three dozen to 500 people, lobbing questions across a crowd that swallowed the building’s lobby. “Still, in that role you could see the Socratic method come out,” Tierney said.

The Socratic method was once as associated with Harvard Law as it was with Socrates, but it has been modified and abandoned over the last half-century, replaced by lecture, voluntary discussion, and advance notice before calling on students.

Socratic waned because it is considered at worst a way to terrorize a class, calling to mind the imperious Professor Kingsfield of “The Paper Chase.” At best, it is exceedingly difficult for faculty to master.

Warren is regarded as one of Harvard’s last practitioners of “hardcore Socratic.” Elena Kagan taught with a similar style and force, before she became solicitor general in 2009 and Supreme Court justice in 2010. “But Elizabeth is, I would say, a more diplomatic person, a more empathetic person, than Elena,” said Richard Parker, a Harvard Law professor since 1974.

Warren invites students to brunch, responds to e-mailed questions with pages of advice and encouragement, and holds office hours at Hauser Hall with her dog, so students can let off steam by taking Otis for a walk.

Otis succeeded Faith, given to Warren by her Commercial Law class in the spring of 1993, following her year as a visiting professor at Harvard from the University of Pennsylvania.

Some in that class had struggled with the distinction between good faith and bona fide purchasers. Warren explained that bona fide purchasers ask relevant questions before a transaction. Good faith purchasers are more like golden retrievers — “empty head, good heart.”

The rest of the semester, whenever the concept came up, a dozen students would shake the Mr.-and-Ms. formalities of Harvard Law and unleash a chorus of barks. The surprise puppy that followed, secretly cleared with Warren’s husband, was a natural gift — as was its name: Faith.

Warren that spring declined an offer to stay at Harvard for personal reasons, but she came around two years later, decamping from Philadelphia for good in 1995.

Warren’s students at Penn revered her, but she was not as universally loved by the faculty as she would become at Harvard, where more than 50 law professors and instructors have contributed to her campaign.

Some at Penn viewed Warren as sharp-elbowed and ambitious. Part of it may have been jealousy over individual achievement at a school hovering around the top 10 but not number one; at Harvard, climbers seeking the peak can exhale.

Warren also focused on academic heft over diversity in hiring, at a time when many top law schools were in turmoil over race, gender, and a new lens for viewing the law known as critical legal studies. By the time she reached Harvard, the rift was healing at a law school dubbed “Beirut on the Charles” in the ’80s.

Warren’s assignments also may have shaped how colleagues viewed her. At Penn, she served on the appointments committee, placing her squarely amid tense faculty meetings over tenure and hiring. At Harvard, Dean Robert Clark assigned her initially to a committee studying student satisfaction, work influencing Harvard’s decisions to halve the size of first-year classes, expand the faculty, and invest in student amenities.

Clark also appointed Warren to the admissions committee; his successor as dean, Kagan, named Warren chair of that committee, the clutch of professors charged with setting the tone for admissions and recruiting top students.

The role was natural for a professor known as a student advocate. Warren’s tenacity was about pushing students to achieve, and her determination to call on everyone in class a recognition that the most eager to speak were not exclusively the brightest.

“She was motivated by equality,” said Katherine Barrett Wiik, a 2005 graduate who worked on a study of women’s experiences at Harvard Law that included extensive surveying and observation; Warren helped facilitate the research. “We all observed that when professors called on [volunteers], there would be a lot more men jumping for air space.”

Warren’s system was about making sure every student learned the material and learned to think like lawyers, said Adam Benforado, who took the contracts class with her as a 1L, later served as her teaching assistant, and is now an assistant law professor at Drexel University.

As the semester advanced, the anxiety in the hall never quite receded. “You were at the edge of your seat not because you felt she was ever going to bite your head off, but because you wanted to please her, and part of that was just respecting how good she was at doing this,” he said.

Outside the classroom, Warren was a “mentorship machine,” said Littwin, the student-turned-Texas professor. She knew that the work of some earlier bankruptcy scholars had fallen from view for lack of academic heirs, and she encouraged successors — without steering them to the academy. She was just as solicitous with students who wanted to apply to law firms or pursue public interest.

Her annual entry in Harvard’s public-interest auction, a graduation barbecue for students at which she promised to whisper nice things to their mothers, often attracted the highest bids.

And though Warren’s scholarship aligned her with consumers against Wall Street, she withheld her personal politics. The morning after the uncertain election of 2000, Warren broke from her bankruptcy curriculum to discuss the Bush-Gore stalemate, never revealing whom she was rooting for, recalled Seth Stern, a 3L in that class.

Benforado shakes his head at the notion that “she’s one of these lefty professors who’s corrupting the minds of impressionable law students.”

“That’s as far from the truth as you can get,” he said. “To the extent that there was an ideological angle on a case, she would always be playing the opposite of whatever the student was in the classroom.”

As Washington pulled Warren farther from the halls of Harvard, she remained invested in students. Sara Sternberg Greene took Warren’s Empirical Legal Studies seminar in spring 2010, while the professor was commuting to the capital.

Warren kept up with each of the 15 or so students as they explored research projects, e-mailing from Washington. “I would type a short paragraph and then I would get back like two pages, usually that day,” Greene said.

Littwin observed that trait in spring 2009, during the height of Warren’s relief program work.

A first-year professor, Littwin was teaching secured credit, using a textbook Warren co-authored, when she struggled to get students to see multiple sides of an ethical issue.

“If you happen to have a spare moment, I’d really appreciate if you could help me think through how to teach this better. By the way, my next class is tomorrow,” Littwin recalled, paraphrasing her note to Warren. “Within two hours, she sent me a thoughtful e-mail about how to set up the problem so that both sides of the issue were salient from the get-go.”

Such gestures continue, even in the consuming heat of the campaign.

Warren had encouraged Greene — a doctoral candidate in sociology and social policy, studying the impact of financial laws on the poor — to consider seeking a home on a law school faculty instead of a sociology department.

Now wading into the job market, Greene found herself in need last month of a short-notice letter of recommendation. But just days before Warren’s first debate with Brown, Greene was reluctant to ask for help. Still, this was for a job opening at a top 10 law school, so she hit send.

That was a Friday evening. Warren replied immediately, happy to help, and e-mailed again the next night. “Strong letter went out today,” she wrote. “Fingers crossed.”

Mary Carmichael of the Globe staff contributed to this report. Eric Moskowitz can be reached at emoskowitz@globe.com.